With masks in short supply during the pandemic, people are questioning whether N95 masks expire. Are expired–but otherwise untouched–N95 masks still effective? Surprising results from a peer-reviewed study have led some to question expiration dates on N95 masks really mean.
Why Do Masks Have Expiration Dates?
Manufacturers mark their masks with expiration dates. For example, 3M says their masks have a 5-year shelf-life when the respirators are stored in their original packing and in proper climate conditions (-4F to 86F, not exceeding 80% RH). That leads some to conclude that masks are less effective after this date.
The motivation behind the expiration date that face masks’ effectiveness depends on having a good fit. Over time, it is possible for the elastic bands and nose pieces to start to degrade. If the straps and other structural pieces are degraded, the masks will fit less well.
Do Expired Masks Perform Worse?
Researchers at the University of North Carolina and the EPA investigated this idea by testing brand new and 10-year-old expired 3M N95 face masks. Importantly, the researchers tested the masks on real people’s faces, rather than manikins.
These fit tests are important because they take into account the part that people most suspect would degrade–the straps and other pieces that influence fit. The test compares the number of particles inside the mask while a person is wearing it versus the number of particles outside the mask.
10-Year-Old N95 Masks as Effective as New
Surprisingly, the expired N95 masks were within one percent as effective as the brand new masks–essentially indistinguishable.
It’s important to note that this was a relatively small study. The researchers tested six different masks in two model numbers. However, there was no evidence of a meaningful reduction in effectiveness.
N95 Masks More Robust than Once Thought
This data adds to other tests finding that N95 masks last longer than some people have thought. Longevity tests have found less than a 1% decrease in fit effectiveness in pollution masks worn every day for 30 days.
A separate non-fit-tested masks prevented infection as well as fit-tested masks. Although formal fit tests and brand-new masks are an ideal, this real-world data suggests that masks are still highly effective under less-than-ideal condition.
Read More: How Long Do N95 Masks Last?